It's highly recommended to use git versions >= 1.5.6 (e.g. 1.5.6.1,
1.6.0.4 a.s.o) if you use/do git merge.
Older versions do not support the merge.log options or git merge --log
and _will_ not generate merge summaries in the merge commit messages
(which are very nice to have).
If you have an older version and you don't want to upgrade try setting
merge.summary (git config merge.summary true).
Andrei